Wrong speed (speedometer vs. GPS)

Very rarely with a car's speedometer agree with the GPS. The GPS is a measurement of time and distance while your car measures rotations of some part. The dealer doesn't want to replace or calibrate the parts as they don't make a lot of money doing warranty work.

I have heard numerous times (and seen) that the speedometer is higher. I suspect it is that way so the driver drives slower. Unfortunately, the driver will in time get used to it and speed up.

I sometime look at my speedometer and the speed on my 3790LMT and it look accurate to me.

My 260 shows me going slower than the speedometer by about 5mph

I compared two different GPS units against my 2009 Nissan Maxima speedo and in both cases the car speedo is approximately 2 mph faster than what the GPS shows.

My 2002 Toyota Camry speedo was dead on.

The Nissan Dealer would not submit under warranty repair.

This has been discussed at length in other threads in this forum. Here are a couple of them:
http://www.poi-factory.com/node/26671
http://www.poi-factory.com/node/6695

You can easily check your speedometer accuracy. Here is a copy of a post from one of the above threads that describes how to do it:

As long I don't see a red and blue light flasing in my rear view mirror, I know that I am not speeding.

Are you sure the Nuivi is higher than the car's speedo? Usually they read low.

The GPS is, on average more accurate than the car's speedo, unless you've had it calibrated.

GPS is, however subject to anomalous operation for a whole bunch of reasons and can be wrong, usually just when you need it to be right . . . .

The speed displayed on my 855 is within 1 mph of the spedometer on my Honda Civic when travelling at a constant speed. Many GPS receivers use the Doppler shift of the received satellite signals to determine speed. The speed computed from the Doppler shift is typically accurate to 0.1 mph. Note that the speed displayed in MapSource from a downloaded track is computed by dividing distance by time and can be inaccurate in many circumstances. I'd trust the GPS speed rather than the speedometer if there is a difference.
Mark

The speed indicated on my 3790LMT and my speedometer are in accord. I drive with cruise control and I can easily see both.

When I tap my cruise control to increase speed by 1 mph, as the car's speed increases so does the indication on my nuvi.

I often use my cruise control to increase or decrease my speed and not use my accelerator.

I am very pleased how they are in agreement.

Gary Hayman

+1 for GPS speed. Mine shows a difference of 10km. I trust the GPS better, rather than one that's based on revolution of the wheels.

I posted in another thread about my GF 2008 Toyota Matrix. The needle and the odometer showed 62 when the GPS showed 60. The 2010 Scion is in total agreement with the GPS in speed and miles traveled. My speedo in the 96 Dodge PU shows 62MPH when GPS shows 60. The miles traveled is the same on a 500 mile trip.

Simple test:

Get someone else with a GPS to "pace" you. See if their GPS agrees with your GPS (probably will).

Getting the dealer to fix it may be a problem though, as the code in the speed unit will have to be changed. You are probably going to have to get Kia involved, if the dealer is not co-operative.

The other thing to consider is that your car's mileage warranty will expire later than it should, if the odometer is off as well. But, you'll need to find a measured km somewhere to check it. You can use the KPs on a highway, but use 5 or more to check the odometer reading as well as the speed as alandb wrote.

The Federeal regulations in the US were +/- 10% for a speedometer and odometer (from the factory), but I'm not sure what they are now, or what they are in Canada, where you live.

In my area, Philadelphia, PA, USA, we have RADAR signs, that will tell you the speed limit and then tell you what your speed is, they look like this:

http://www.radarsign.com/Pages/ImageLibrary/regulatorySign/2...

Everytime I have gone by one of these the sign and my GPS have the same speed, most of the time the speedo is off by 5 or so MPH. (I use my GPS in more then one vehicle)

(I'm talking about actual speed comparison, not the feature where Garmin guesses what the limit on the road is)

Being a Ford tech, I know when recalibrating any FMC product, you mainly have a few choices of tire sizes and diff gear ratios for each model. It gets interesting when the "modified" trucks come in.

Use a 12 volt splitter and use 2 nuvis side by side.

Thought about having 2 in one vehicle and comparing. Splitter not needed if battery of one is in good shape.

My 2009 G37 got between 2-5 mph different with the 3790.

While my 2011 Sienna got at least 5-8 mph different.

I stick with my car speedometer since it easier to keep an eye on and within 5-10 mph range so I don't get a speeding ticket.

If you replace your tires with a larger or smaller diameter than the ones that came with the car, you speedometer will be off the speed the car is really going.
If you change the size of the tire you have to replace the gear that goes into the transmision.
That is where the speed is read from. This site shows how it works

http://www.transmissioncenter.net/speedometer_calibration___...

I have an Acura which always shows 2 - 4 kilometers faster than the GPS. I have driven with a 330, 780 and 1490 at the same time. GPS always show the same speed, car is always higher.

Honda has acknowledged that certain model year products speedometers read higher than actual, and subsequently the warranty expired on mileage earlier than it should have. Honda settled this one out of court.

No wonder my Altima reads 5 miles faster than my Nuvi
http://www.cbsnews.com/stories/2007/03/13/earlyshow/main2562...

Besides being cheated on warranty and re-sale value you are being influenced to buy one brand over another based on MPG claimed.

Isn’t the government mandating MPG, how do they let the car manufactures get away with the scam?

My 765t shows speed is always about 1-2mph slower at highway speeds than my pontiac shows. I believe GPS is accurate. This is the way that I would expect car to be calibrated. (conservative)

My basic Etrex H spec quotes accuracy of 0.1 knot, so shouldn't think other Garmin GPS's would be any different. So GPS is more accurate.

The Electronic Speedometer
An electronic speedometer receives its data from a vehicle speed sensor (VSS), not a drive cable. The VSS is mounted to the transmission output shaft or to the crankshaft and consists of a toothed metal disk and a stationary detector that covers a magnetic coil. As the teeth move past the coil, they "interrupt" the magnetic field, creating a series of pulses that are sent to a computer. For each 40,000 pulses from the VSS, the trip and total odometers increase by one mile. Speed is also determined from the input pulse frequency. Circuit electronics in the car are designed to display the speed either on a digital screen or on a typical analog system with a needle and dial.

Speedometer Accuracy

No speedometer can be 100 percent accurate. In fact, most manufacturers build speedometers so they fall within a fairly narrow tolerance range, no more than 1 percent to 5 percent too slow or too fast. As long as a car is maintained at factory specs, its speedometer should continue to register vehicle speed within this range. But, if a car is modified, its speedometer may need to be recalibrated.

Changing tire size is one of the most common things car owners do that can affect speedometer accuracy. That’s because larger tires cover more ground in one complete revolution. Consider the example below.

Your car comes with factory-installed tires that are 21.8 inches in diameter. That means the circumference of each tire is 68.5 inches. Now let’s say you want to replace the stock tires with new tires that are 24.6 inches in diameter. Each new tire has a circumference of 77.3 inches, which means it travels almost 10 inches farther with each complete revolution. This has a tremendous affect on your speedometer, which will now indicate a speed that is too slow by almost 13 percent. When your speedometer reads 60 miles per hour, your car will actually be traveling 67.7 miles per hour!

The first is speedometer accuracy;

There are no federal laws in the US that specify accuracy in passenger vehicles (commercial vehicles need to be +/- 10%), though automotive engineers voluntarily adhere to either SAE or Euro specifications (their choice, though I have no idea which any individual manufacturer may have chosen).

The psychology of making optimistic speedometers is simple to understand; You will drive slower if you believe that your vehicle is going faster . . . however if you are driving in a 65 mph zone with cruise set to 65 and your speedo is off by 10%, then you are going 58.5 mph and likely creating a traffic jam.

The second is odometer accuracy;

The law does require that odometers be 'reasonably accurate'. I can't find a formal specification for acceptable tolerance; But there were/are a couple of class action suits against Honda and Nissan for apparently delivering readings that were too high by 2% with new tires(, where they should have read 'low' because tire circumference is greatest when the tires are new). Manufacturers and leasing companies would benefit from premature expiry of warranties and the recording of excess mileage under leasing contracts.

It isn't hard to create an optimistic speedometer and couple it to an accurate odometer. However what would be appropriate (and safest) is if everyone's speedometers read the same.

My Garmin is always displaying 5MPH slower compared to my cars speedometer.

Both of my Toyotas matched my GPSs until I replaced the tires on my wife's car with a wider and lower profie tire and now there is a 2 MPH difference. To see what tires size does, use the Discount Tire site as it has a comparer that tells you what to expect in MPH changes based on tire size. My 2 MPH was as they predicted.

My Camry matches exactly the GPS speed. My Sonata is 5 km/h slower than the GPS. I kind of like it as it prevents me from speeding too much.

My Chevy Impala always showed right on with either GPS and so does my Chevy Equinox. My wife's Pontiac Vibe shows about two MPH slower then either GPS.

Here is what VW says about speedometer on my 2010 Jetta TDI Sportwagon:

"German cars allow the speedometer to read fast by a tenth of true speed plus 4 kph but never slow. The error may be higher or lower depending on wheel/tire sizes. "

For me the GPS speed indicator is the only one I look at.

I believe my TomTom. Both my car and my RV speedometers read several kph faster on the highway.

Have used a Nuvi 2350 and an Escort 9500ix that have GPS speeds. Both have been right on for my Acura TL.

auto makers want the speedometer to be faster so that you use up you warranty quicker even though you have probably driven fewer miles.

I've checked my speedo with those laser speed limit signs that are located at various places around town. I've compared it to 5 different lasers and each one indicates that my speedo reads higher than my actual speed, i.e., I have my cruise control set to 45mph and the lasers show that I'm going 43mph. When I check the Garmin it shows that I'm 1 to 2 mph over what my speedometer is reading. This is in city driving and not sure if it's more or less accurate if I were on a freeway or not.

The speedometer of my Suzuki Grand Vitara matches the GPS when going a steady speed (on speed changes the GPS lags more). My BMW is 2-3 mph faster on the speedometer than it is in real life (GPS). This is a known and documented issue with BMWs. There is apparently a law in Germany that the speedometer cannot read less than the actual. So they set up the speedometer to never be low for any tire that will fit in the wheel-well. BMW does not allow the dealer to "fix" it. The speedometer is one of amny things that is essentially determined by a computer program. That makes it particularly frustrating that it cannot simple be fixed. Germans are quite inflexible in their logic. I ignore the speedometer and just look at the 885t to determine how fast I am going.

With the Honda class action suit being so prominent a few years back (it was settled) I am surprised that so many people are unaware of many mfgs setting the speedometer and the odometer to read higher than actual by a couple of percent. Honda claimed that they were within the percentage allowed by ISO and industry standards.

The ones who originally got hit the most were the people who were "over" their lease mileage!!

my 765 runs 2 mph slower than my speedometer on both cars (2002 Nissan Frontier & 2010 Audi A4) I use it in, ver consistent

My GPS reads 5mph slower than one of my vehicles, right on with the Rav 4 (new tires).

I have found my 765T to be accurate if the roadside speed notifications signs are correct. There are quite a few in my area that advise drivers of their current speed. Generally my 765T will be spot on with the advisory sign whereas my 2000 Honda Insight will show one to two MPH higher.

My Honda Civic speedo reads about 6% high compared to my GPS (even with original size tires). Since my car is 17 years old with 1/4 million km and had no warranty claims I don't feel cheated too badly that my warranty expired 6% early.

If it reads 6% higher then your Honda has not traveled ¼ million kilometers, your speedo is lying to you.

Prior to having my 255W I did check my speedometer (and odometer) against mileposts over a 10 mile span and it was accurate within 1 mph. The speed on my speedometer and the speed on my 255W almost always are within 1 mph except when first accelerating or while coming to a stop.

My car shows its speed on the console LCD screen, and it matches my 265w dead on.

My BMW speedo is showing me 4 mph higher than acutal speed...

the speedometer on my Mazda3. I kind of wish the gps would show 5 lower. I could plead the extra 5 came from using the gps speed. Silly me. They are only going to go by what they clocked.

Here on the Canadian Prairies we have a 1350LTM.

2003 VW Passat 110kmh = 107gps
2011 Ford Edge 110kmh = 107gps

That's close enough for us

for 2 independant sources to show the same reading.

Reminds me of a saying: "A man with one watch always knows what time it is, but a man with two watches is never sure."

My jeep runs 3 miles over the speed. but eh gps is right on. Had it check by a local deputy sheriff.

The 2 Nuvi's I have show going slower that the speedometer, by about 3 mph. but only at certain speeds!